1. Field of the Invention
The invention relates to a method for assembling a position measuring device, and to a positioning device for setting the scanning distance of a position measuring device.
2. Description of the Related Art
In position measuring devices, a scale is scanned by a scanning element. In this scanning, position-dependent electrical scanning signals are obtained that are delivered to a following electronic device, such as a counter, or a numerical controller. The quality of the scanning signals depends on the scanning distance, and it is therefore necessary to install the scanning element at a precisely defined distance relative to the scale.
In European Patent Disclosure EP 0 177 711 B1, a position measuring device is described in which a scanning element in the form of a scanning division is displaceably supported in a guide for setting the scanning distance and can be stopped in every position. The requisite scanning distance is predetermined by a spacing foil that is inserted during the assembly between the scale and the scanning division. The displacement of the scanning division takes place until clamping of the foil; after that, the scanning division is fixed, and the foil is removed.
A disadvantage of this known position measuring device is the necessity of a separate foil as a spacer and of laterally removing a clamped foil.
In European Patent Disclosure EP 0 280 390 A1, a position measuring device in the form of a rotary transducer that has no bearing of its own is known. Such rotary transducers are known as built-in rotary transducers. In built-in rotary transducers, the relative position of the scanning unit and the disk is not defined until the transducer has been mounted on the objects to be measured. To simplify this attachment, a fixation element is integrated with the rotary transducer and is contact with the hub of the disk and defines the position of the disk during the attachment process. Once the disk has been mounted on the one object to be measured and the scanning unit has been mounted on the other object to be measured, the fixation element is removed from the hub.
From European Patent Disclosure EP 0 841 539 A1, a position measuring device is known in which a scanning element is supported on a support displaceably from a first reference position to a second reference position. For the displacement, a positioning device is integrated with the support, and with the positioning device the scanning element, after the mounting of the support on an object to be measured, is moved from the first reference position to the second reference position.
This method has the disadvantage that a positioning device must be integrated with every position measuring device, and that the scanning element must be movably supported on the support.
It is therefore the object of an present invention to disclose a method with which simple mounting and adjustment of a scanning element relative to a scale are assured.
The above object and advantage is attained by a method for assembling a position measuring device, in which a scanning element is fastened to a first object, and a scale including a measurement division is fastened to a further object, the fastening being done while maintaining a predetermined scanning distance between the measurement division and the scanning element. The scanning distance is set by positioning the scanning element at a first reference position relative to the scale, positioning first and second parts of a positioning device at a first reference position, fixing the first part of the positioning device directly or indirectly to the scale and fixing the second part of the positioning device directly or indirectly to the scanning element in a direction of motion along the scanning distance. Moving the first part of the positioning device relative to the second part of the positioning device by a predetermined distance in the direction of the scanning distance so that the scanning element is put into a second reference position relative to the scale, in which position the requisite scanning distance is accomplished.
Another object is to disclose a positioning device with which the requisite scanning distance can be set in a simple way during assembly.
The above object and advantage is attained by a positioning device for setting the scanning distance between a scanning element and a scale of a position measuring device, the positioning device including a first part that is fixed in at least one direction of motion along a scanning distance directly or indirectly to the scale and a second part is fixed in at least one direction of motion along the scanning distance directly or indirectly to the scanning element, wherein the first or second part is displaceable relative to the other part in the direction of the scanning distance, and the displacement distance is defined. The first or second part includes a receptacle that is clamped to a face, extending in the direction of the scanning distance, of the scale or to a support of the scale, or to the scanning element or to a support of the scanning element.
Other advantages of the present invention are in particular that the scanning distance can be set by a positioning device that can be used for many position measuring devices. The position measuring device itself can be simple and economical in structure.
The present invention will be described in detail in terms of exemplary embodiments.
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